Why is it bad to say you smell bacon around a cop?

Years ago police were referred to as "PIGS" to insult and demean them.

"Bacon" will probably be interpreted by the officer as an attempt to call them a PIG without you being brave or honest enough to say it to them directly.

Because they will very likely take offense (whether or not they show it) and find creative but legal ways to make you regret your attempt at being funny.